Patients with chronic disease often see a multitude of outpatient providers. For example, Medicare beneficiaries with coronary artery disease each see a median of 10 physicians (3 primary care physicians and 7 specialists) in 6 different practices each year. Seeing more than one physician may be clinically appropriate and indeed may be necessary in order to receive recommended care. However, highly fragmented care increases the risk of gaps in communication across providers. Prior studies suggest that more fragmented care can lead to suboptimal care, with more adverse drug interactions, more testing, more procedures, and lower patient satisfaction, compared to less fragmented care. However, which patients are at greatest risk for healthcare fragmentation and how fragmentation affects patient outcomes are not known. In addition, individuals' experiences of fragmented care are poorly understood, even though understanding individuals' experiences is critical for identifying potential solutions. The overall objective of this proposal is to determine the association between healthcare fragmentation and cardiovascular outcomes, by conducting an ancillary study to the REasons for Geographic and Racial Differences in Stroke (REGARDS) study. REGARDS is a national, NIH-funded prospective cohort study, which began in 2003 and is ongoing. It includes detailed data on participants' demographic characteristics, co- morbidities, psychosocial variables, and adjudicated myocardial infarction and stroke outcomes. The proposed project will include a subset of 7,120 participants for whom REGARDS data have been linked to Medicare claims at baseline. Fragmentation will be measured from claims, primarily using the Bice-Boxerman Index, a commonly used measure of fragmentation that captures both ?dispersion? (the spread of a patient's care across multiple providers) and ?density? (the relative share of visits by each provider). Fragmentation will also be measured through participant surveys, using a measure previously validated in a Medicare population. The specific aims include determining: 1) which participants are at highest risk of having healthcare fragmentation, 2) associations between claims-based fragmentation and outcomes, and 3) associations between self-reported fragmentation and outcomes. The outcomes of interest include myocardial infarction, stroke, death, emergency department visits, hospitalizations, and healthcare expenditures. This study represents an innovative use of a large cohort to understand the problem of healthcare fragmentation. The research team is highly experienced and multidisciplinary, with national experts in cardiovascular epidemiology and healthcare delivery. Results from the proposed study can be used to inform the design of future interventions to decrease fragmentation and improve outcomes.